Organic pesticides persistence

Sustainable strategies for monitoring, assessment and management of persistent organic pesticides (WONG Minghung, China)... 

Why is this important It is important because it has a direct impact on the meaning of USDA certified organic foods. In order to receive a USDA certification as an organic food, the food producer must not have used pesticides for the previous three years. However, as evidenced by the food data collected by the FDA, banned pesticides persist in the soil to this very day. Furthermore, the vast majority (i.e., about 95 percent) of the food sold in the United States is grown and produced in the United States. This means that those foods found to contain banned pesticides had to come from farms in the United States. 

The environmental persistence of DDT and its immediate metabolite DDE is characteristic of chlorinated organic pesticides as a class. 

To appraise the extent of environmental contamination is a problem in organic pesticide analysis. Analytical methods for such diverse samples as air and human tissue have been developed and are yielding important information. The fate and persistence of pesticides constitutes another complex problem. It includes consideration of environmental and biological effects upon pesticides, how they move in rivers, and how they are translocated from one environmental medium to another. Finally, there is the question of damage control. Can we reduce the introduction of pesticides into air and water If not, can we effectively remove these poisons from the parts we consume ... 

Approximately 300 organic pesticide chemicals are being marketed in more than 10,000 different formulations. Last year over 750 million pounds were used in the United States. Insecticides account for nearly half this amount, but herbicides will far surpass them in tonnage within a few years. The chlorinated hydrocarbon insecticides have attracted attention because of their so-called persistence However, unlike some of their inorganic predecessors, organic pesticides are decomposed in the environment by biological and physicochemical processes which influence the amounts that will be found in the environment. Their mere presence in the environment does not necessarily jeopardize the public health. The amounts present, their toxicities, and the rate of detoxification and decomposition must be considered to assess their significance in the environment... 

All manner of pollutants are considered under the discipline of terrestrial ecotoxicology including pesticides, persistent organic pollutants, other organic substances, and metals and metalloids (e.g., selenium and arsenic). Naturally occurring toxins such as those produced by poisonous plants, snakes, or invertebrates generally are not included unless people intentionally apply them for pest control. For example, the pyrethroid pesticides are derived from the naturally occurring pyrethrin toxin that is found in chrysanthemum. 

The presence of organic substances and clay particles increases pesticide persistence in the soil. This is a result of an increased adsorption of these substances on humus and clay particles. As a result of this, pesticides become a suitable substrate for the activity of soil microorganisms. The rate of their evaporation and washing out is decreased. 

Technology for removing organic pesticides from water has not paced the problems that have resulted from the increased quantities used, new products and formulations placed on the markets, and new sources for their entry into the environment. Some organic pesticides are resistant or unaflFected by conventional water and wastewater treatment practices (IJ). Also, many organic pesticides resist biological degradation in aquatic environments, hence they may persist for some time (7, 12, 13, 14). 

Which word can be used to describe organic pesticides that are not readily biodegradable (a) Permanent, (b) Persistent, (c) Nonvolatile. 

Attempts to couple electrochemical ozonisers with UV light have been investigated [75]. When dissolved ozone is irradiated with 254 nm wavelength UV light, a photo-enhanced oxidation process occurs due to the increased reactivity caused by the hydroxyl radical (which is formed by photolysis of the ozone). This method totally oxidises a wide range of persistent organics (pesticides, polychlorinated-biphenyls) and pyrogens. 

Persistence of pesticides in the environment is controlled by retention, degradation, and transport processes and their interaction. Retention refers to the abihty of the soil to bind a pesticide, preventing its movement either within or outside of the soil matrix. Retention primarily refers to the sorption process, but also includes absorption into the soil matrix and soil organisms, both plants and microorganisms. In contrast to degradation that decreases the absolute amount of the pesticide in the environment, sorption processes do not affect the total amount of pesticide present in the soil but can decrease the amount available for transformation or transport. 

Many factors affect the mechanisms and kinetics of sorption and transport processes. For instance, differences in the chemical stmcture and properties, ie, ionizahility, solubiUty in water, vapor pressure, and polarity, between pesticides affect their behavior in the environment through effects on sorption and transport processes. Differences in soil properties, ie, pH and percentage of organic carbon and clay contents, and soil conditions, ie, moisture content and landscape position climatic conditions, ie, temperature, precipitation, and radiation and cultural practices, ie, crop and tillage, can all modify the behavior of the pesticide in soils. Persistence of a pesticide in soil is a consequence of a complex interaction of processes. Because the persistence of a pesticide can govern its availabiUty and efficacy for pest control, as weU as its potential for adverse environmental impacts, knowledge of the basic processes is necessary if the benefits of the pesticide ate to be maximized. 

Air-poUutant effects on neural and sensory functions in humans vary widely. Odorous pollutants cause only minor annoyance yet, if persistent, they can lead to irritation, emotional upset, anorexia, and mental depression. Carbon monoxide can cause death secondary to the depression of the respiratory centers of the central nervous system. Short of death, repeated and prolonged exposure to carbon monoxide can alter sensory protection, temporal perception, and higher mental functions. Lipid-soluble aerosols can enter the body and be absorbed in the lipids of the central nervous system. Once there, their effects may persist long after the initial contact has been removed. Examples of agents of long-term chronic effects are organic phosphate pesticides and aerosols carrying the metals lead, mercury, and cadmium. 

The methods, which allow in one procedure of analysis to overcome, for example, most pesticides which are used in agricultural practice in the present time, get development and introduction in practice. The contribution of the Ukrainian scientists in field of chromatographic analysis of Persistent Organic Pollutants (POPs, chlorinated hydrocarbons, PCB s) and supertoxicants, such as PCDDs, is estimated. 

Jury WA, Spencer WF, Farmer WJ. 1983. Use ofmodels for assessing relative volatility, mobility, and persistence of pesticides and other trace organics in soil systems. In SaxenaJ, ed. Hazard assessment of chemicals Current developments. Vol. 2, New York, NY Academic Press, 1-43. 

Frank R, Braun HE, Ishida K, et al. 1976. Persistent organic and inorgaiuc pesticide residues in orchard soils and vineyards of Southern Ontario. Can J Soil Sci 56 463-484. 

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